i have a mast_user table with 20 records......i have prepared a form which updates a particular record successfully......but something pinches me here......it updates username of the table and the user can assign the existing username to his record......

I mean i want to add a validation code which says "username already exists....please update with a different username if u really want to change"
but i cant figure out...where to add this...especially when the variables are sent by GET method.......ie passes thru querystring into the other file where GET_VARS are there.

i also dont want the common user to avoid changing the administrator details.....i mean how shud i do it.......the third file is coded by me as follows where update is executed....

i did not get the related solution from u.........me thinks u have misunderstood mmy problem......plz read it carefully......i want only validation suggesstions from u......Anyways thanku very much for ur prompt response...............